1. Field of the Invention
The present invention relates to a transmitting apparatus and a channel speed varying method and, more particularly to a transmitting apparatus and a channel speed varying method that can automatically reduce the speed of a channel by implementing Link Capacity Adjustment Scheme (LCAS) to improve the quality of the network.
2. Description of the Related Art
Link capacity adjustment scheme (LCAS) as a technology has come into focus for its role in improving the transmission quality of a Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH, hereinafter, simply “SDH”) network using virtual concatenation (see, for example, Japanese Patent Laid-Open Publication No. 2006-13562).
Virtual concatenation refers to a technology that allows a plurality of SDH channels to be integrated as a single virtually concatenated group. LCAS is a technology that allows dynamically linking channels to or dropping channels from the virtually concatenated group.
By combining LCAS with virtual concatenation, a new channel can be added when the speed of the virtually concatenated group needs to be increased, without interrupting the ongoing transmission and without in any way affecting the operations in the existing channels.
The LCAS can be similarly employed to drop failed channels from the virtually concatenated group. The channel speed in this case is automatically reduced, but the channels are operational albeit at a reduced speed. In the absence of LCAS, failed links will render the entire virtually concatenated group dysfunctional.
The SDH network is generally used as a backbone of a large-scale network. Generally, the network to which the terminal of an end user is connected is usually an easily manageable Ethernet™ (hereinafter, simply “Ethernet”) and a high-speed SDH network connects all the Ethernet networks.
In such a setup, at times the dynamic change in the channel speed brought about by LCAS may not produce effective results. Thus, to increase channel quality, routers are provided on the Ethernet network that allow, by a priority control function, frames (packets) of a specific user or specific frames to be carried over the channel. However, LCAS dynamically changes the speed of the virtually concatenated group independently of the priority control set by the routers.
Therefore, when some channels of the virtually concatenated SDH channel group fail, even though LCAS takes care that the normally functioning channels of the virtually concatenated SDH channel group do the job, the channel speed is reduced by the LCAS without regard to the priority control set at the Ethernet end. As a result, the channel speed of the SDH network falls below the speed required for transferring the Ethernet frame, resulting in frame loss regardless of the priority control, which causes a significant reduction in the channel quality.